1. The Earthiest

Kepler-78b is most similar to Earth in mass, diameter and composition; it could be made of rock with an iron core. But it’s no Earth analog, whizzing around its star in 8.5 hours, with temperatures exceeding 2,000° Celsius (SN Online: 10/30/13).

2. The wettest

HR 8799c’s atmosphere lacks methane, which could signal life, but does have water and carbon monoxide (SN: 4/6/13, p. 5). Water has also been found in the atmospheres of WASP-17b, HD209458b, WASP-12b, WASP-19b and XO-1b.

3. The rogue

Planetary candidate PSO J318.5-22 has no parent star. The object is roughly six times the mass of Jupiter, has features similar to other directly imaged exoplanets, including HR 8799c, but floats through space all alone (SN Online: 10/9/13).

4. The runt

Kepler-37b is the littlest planet found to date. At 3,860 kilometers across, the exoplanet is about 30 percent of the diameter of Earth or 80 percent the width of Mercury (SN Online: 2/20/13).